Integrated circuit switches used in 3D and other integrated circuits can be formed from solid state structures (e.g., transistors) or passive wires (MEMS). MEMS switches are typically employed because of their almost ideal isolation, which is a critical requirement for wireless radio applications where they are used for mode switching of power amplifiers (PAs).
MEMS can be manufactured in a number of ways using a number of different tools. In general, though, the methodologies and tools are used to form small structures with dimensions in the micrometer scale. Also, many of the methodologies, i.e., technologies, employed to manufacture MEMS have been adopted from integrated circuit (IC) technology. For example, almost all MEMS are built on wafers and are realized in thin films of materials patterned by photolithographic processes. More specifically, the fabrication of MEMS use three basic building blocks: (i) deposition of thin films of material on a substrate, (ii) applying a patterned mask on top of the films by photolithographic imaging, and (iii) etching the films selectively to the mask.
Depending on the particular application and engineering criteria, MEMS structures can come in many different forms. For example, MEMS can be realized in the form of a single cantilever structure such as, for example, shown in U.S. Pat. No. 7,265,492. In this cantilever application, a single cantilever arm (suspended electrode) is pulled toward a fixed electrode by application of a voltage. In known applications, the voltage required to pull the suspended electrode down to the fixed electrode by electrostatic force may be high, which has been seen to cause unwanted charging on insulator after prolonged use and eventual failure of the switch. In certain applications, the high voltage, e.g., 100 volts, is also difficult to obtain since this has to be stepped up from about 1.5 volts to about 5 volts. The minimum voltage required is called pull-in voltage, which is dependent on area of the electrode, spacing or gap between the suspended and fixed electrodes, and spring constant of the membrane or springs.
Lowering the pull-in voltage without decreasing the gap and without softening the spring is desirable, as the spring provides the restoring force and determines the switching speed. In U.S. Pat. No. 7,265,492, a pair of side parallel-plate electrostatic actuators is implemented for lowering or eliminating of the bias voltages. These additional electrostatic actuators are used to reduce or eliminate the bias voltage to be applied on the fixed signal electrode. In implementation, the fixed electrode of the side parallel-plate electrostatic actuators can be elevated above a fixed signal electrode. Thus due to a smaller gap, the pull-in voltage required to pull the suspended electrode down to the fixed electrode can be lowered. However, the MEMS shown in U.S. Pat. No. 7,265,492 are not hermetically sealed, and the additional electrostatic actuators can increase fabrication costs.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.